Based on the following Tree Data Structure, answer the questions $(12,13$ and $14)$:

$12.$ Which node is a sibling of node $6?$

C$)7$

A$)10$

D$)9$

B$)5$ and $11$

$13.$ How many internal nodes are in the tree?

C$)4$

A$)10$

D$)1$

B$)5$

$14.$ What is the height of the tree?

A$)6$

C$)4$

B$)2$

D$)3$